Flywheel energy storage devices and systems are known for storing energy and releasing stored energy on demand. Known flywheel assemblies have a traditional rotor design sometimes made with carbon fiber composites. Such rotors have a shaft on which the motor/generator (M/G) and bearing permanent magnets (PMs) are mounted. The shaft is conventionally connected to the rim via a hub. The shaft-and-hub flywheel design is limited in terms of its achievable upper-end velocity. Matching useable materials for components in the flywheel assembly has been problematic since the radial growth of the components varies as the rotor velocity increases. The hub must mechanically couple the shaft to the rim without introducing bending modes into the rotor structure through the range of operating frequencies in the operating speed range of the flywheel. However, the shaft often exhibits negligible radial growth while the rim exhibits significant radial growth.
The higher speeds for flywheels enabled by the use of ever-advancing materials unfortunately exacerbates the growth-matching problem for the hub as the increased radial growth of the rim outpaces any growth exhibited by other connected components such as, for example, the connecting shaft. Further, the overall efficiency afforded by flywheel technology is limited by the presently available materials that fail when the flywheel is run at speeds that exceed material tolerances.
In addition, while a high energy density is desired to achieve the maximum energy storage and deployment, the energy density that is achievable in known flywheel assemblies is limited. Further, it is often difficult to reach a flywheel system's energy storage and deployment maximum capacity due to the existence of net angular momentum, and space restrictions often prohibit the usefulness of flywheel technology.